The invention relates to a surface luminaire with a luminous chamber in the form of a hollow fiberoptic conductor with a peripheral frame, an emission opening and a base plate populated at least partially with light-emitting diodes.
Luminous means referred to as light-emitting diodes or LEDs provide the possibility of producing flat spotlights which emit light homogeneously over the surface and which can be used in relatively large design forms in the form of surface luminaires with the designations “softlight”, “filllight” or reflector lamps in all sectors of professional lighting, as portrait luminaires in the immediate vicinity of a moving picture or video camera, in narrow areas, such as vehicles and stairwells, for example, and for constructing light walls in event and stage lighting.
Surface luminaires with light-emitting diodes as the luminous means have different designs. In a first design, a number of light-emitting diodes are arranged on the base of a luminous chamber in the form of a hollow fiberoptic conductor, which luminous chamber has reflecting walls and a diffusely transmitting cover. The light-emitting diodes radiate into the hemisphere above the base of the luminous chamber, with the light emitted by them being reflected a plurality of times diffusely and emerging from the surface luminaire with a large one-half-peak spread. The light-emitting diodes used here can have different diffusion characteristics such as “Lambertian”, “batwing” or “side-emitting” diffusion characteristics, for example, it being possible to achieve a low physical height of the surface luminaire in particular when using side-emitting light-emitting diodes.
In a further design, light is radiated into a solid fiberoptic conductor, for example an acrylic block, surrounding the light-emitting diodes by a number of light-emitting diodes with a side-emitting characteristic which are arranged on the base of a luminous chamber, whereby the light mixing takes place within the solid fiberoptic conductor.
In another design, a number of light-emitting diodes are arranged on the inner edge of a housing frame, with the result that the light emitted by the light-emitting diodes is emitted towards the inside into a hollow chamber or in particular into a solid fiberoptic conductor.
DE 20 2004 016 637 U1 has disclosed a lighting device with a mount, on which a plurality of light-emitting diodes and control apparatuses are arranged, with which the operating state of the lighting device is adjusted. High-power light-emitting diodes with an optical efficiency of at least 20 lm/W which emit in particular white light and are referred to as “Golden Dragon” light-emitting diodes are used as the light-emitting diodes. Drive electronics with a light sensor which measures the ambient brightness and controls the brightness of the light-emitting diodes are used as the control apparatuses.
The use of such a lighting device in a surface luminaire has the disadvantage that the control apparatuses together with the light-emitting diodes are arranged on the mount and consequently reduce the light-emitting area of the lighting device.
The other designs mentioned above also have the disadvantage that the control electronics required for driving the light-emitting diodes need to be fitted outside the luminous chamber, with the result that the advantage of producing surface luminaires with a small physical height with the aid of light-emitting diodes is restricted by virtue of the fact that the control electronics either need to be arranged beneath the light-emitting diodes in order to keep the area which does not emit light as small as possible or by virtue of the fact that, in order to provide flat designs, the light-emitting diodes need to be arranged in the housing frame, which results in a relatively large, non-illuminating edge of the surface luminaire, however.
A further problem in the production of surface luminaires with a small physical height with at the same time a light-emitting area which is as large as possible consists in the fact that the heat emitted by the light-emitting diodes needs to be dissipated reliably for permanently stable operation. This applies in particular in the case of high-power light-emitting diodes which are embedded in a thermoplastic element containing the emission optical element.